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babysit gate reads trusted actors and admission rules by branch name, not a resolved commit #10648
Description
Problem
The babysit merge gate reads trust and policy files from the base branch by name, not by a resolved commit:
plugins/source-control/skills/babysit-prs/scripts/babysit_verify_evidence.py:1400readscontents/.github/standards/trusted-actors/trusted-actors.json?ref={self.branch}.babysit_verify_evidence.py:1465readsADMISSION_RULES_PATHwith?ref={default}.
GitHub resolves a ref that names both a branch and a tag in a way this code does not control (UNVERIFIED which wins for the contents API). If a tag named like the default branch can be created, it could stand in for the branch and supply a different trusted-actor list or admission rules. #10596 closed the same class in the approval-carry and cost-carry compares by resolving the base once to its tip SHA (baseTip / base_tip); these reads were outside that PR.
Fix
Resolve the default branch to its tip SHA once (GET /repos/{repo}/git/ref/heads/{branch}, require a 40-hex object.sha, fail closed otherwise) and read both files at that SHA. Reuse base_tip from babysit_merge_policy.py rather than adding a second resolver.
Optional hardening, a settings change for the owner: a tag ruleset that blocks tags named like protected branches would close this class repository-wide.
Acceptance
- Both reads name a 40-hex SHA, never a branch name; a test asserts the request paths.
- An unreadable or non-commit ref fails closed (no trusted actors, admission refused), with a test.
Refs: #10596
Activity
github-actions commentedon Oct 28, 2026
Proposed work class: work-class: scoped
Basis: automated intake triage; the lanes App applied this class.
Size: Small
Complexity: Low
Uncertainty: Known
Flags: none
Blocked by: none
Understood: the babysit gate reads the trusted-actors file and the admission rules by branch name. You want it to resolve the default branch to its tip SHA once, reusing
base_tip, and read both files at that SHA. An unresolvable ref should fail closed. Acceptance is tests that assert the request paths and the fail-closed behavior. The tag-ruleset hardening is a separate owner settings decision and isn't part of this change. I found no likely duplicate among the open issues.Automated triage, applied by the lanes App.
melodic-automation-lanes commentedon Oct 28, 2026
Not admitted to the issue lane: no trusted-human acceptance criteria: a listed human must put the confirmed
- [ ]criteria in the body or post them as their own comment, or, on an issue a listed human filed, intake's newest refinement comment must hold them unedited. Admission takes the issue once each of those is met, when intake triages it again (.github/actions/resolve-config/admission-rules.json).melodic-automation-lanes commentedon Oct 28, 2026
The latest triage verdict holds nothing: admission moved the issue to
status: confirmed; its comment says why.melodic-automation-lanes commentedon Oct 28, 2026
Refinement. A read-only run explored this repository, searched its issues and pull requests, and read the allowed docs to draft what follows. On an issue a listed human filed, it counts as the issue's spec once posted, while unedited; it is still model text, so check it.
Intended outcome: Both babysit_verify_evidence.py reads (trusted actors, admission rules) name a 40-hex tip SHA resolved via git/ref/heads, failing closed when it cannot be resolved.
Related work
Open questions
RECOMMENDED: Add one small tip resolver in babysit_merge_policy.py, modeled on PostMerge._branch_tip, that uses git/ref/heads, requires a 40-hex object.sha and raises PolicyReadError. Call it from babysit_verify_evidence.py. Do not reuse _default_branch_head, which reads commits/{branch} (still by name). Basis: plugins/source-control/skills/babysit-prs/scripts/babysit_merge_policy.py:4100 and babysit_postmerge.py:1752
RECOMMENDED: Resolve self.branch to its tip for the trusted-actors read, and the default branch via merge_policy._default_branch for the admission-rules read. Keep each at its current branch semantics. Basis: plugins/source-control/skills/babysit-prs/scripts/babysit_verify_evidence.py:1400, 1450-1465, 2949
RECOMMENDED: Keep the branch-name keys, since entries only live for run_cache.MAX_AGE. Resolve the SHA only on a cache miss, and test that a cache hit makes no extra request. Basis: plugins/source-control/skills/babysit-prs/scripts/babysit_verify_evidence.py:1392, 1431, 1453
Sources read
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